In the present context, lines should be taken to mean all flow paths for fluid media. Thus, these include not only flexible hoses or rigid lines but also channels, flow chambers or even just through openings machined into bodies. In the case of through openings, the axial extent thereof thus specifies the length of the line thereby formed. In principle, the length of a line can be very short in complex systems and, in the case of through openings, can be just 1 mm, for example, depending on the thickness of the material of the element having the through opening.
Coating systems of this kind are used to coat objects such as vehicle bodies or body components with the aid of electrostatically operating application devices, for example in the automotive industry. In this context, the coating material, e.g. a paint, is dispensed by the dispensing arrangement and subjected to an electric field, in which the coating material dispensed is ionized and transferred by virtue of electrostatic forces to the object, which, for this purpose, is at ground potential, for example. An application device of this kind can, for example, be a high-speed rotary atomizer, in which the dispensing arrangement comprises a rotating bell-shaped plate, from which extremely small paint droplets are thrown, thus forming a paint mist.
If an object is to be painted in a different color than the previously coated object, a color change must be performed. To enable a color change to be carried out as quickly as possible and without loss of time, a coating system of the type stated at the outset comprises at least two feed reservoirs, thus allowing alternate operation. In practice, this means that the application device is fed with one first coating material from one feed reservoir, while the other feed reservoir can be loaded with a different coating material, thus ensuring that the system is ready for a color change.
In electrostatically operating systems, the lines must build up an insulating section in a direction away from the application device during the coating process, and must be clean and dry to achieve this. The lines are accordingly manufactured from an electrically insulating material.
In principle, it is important in coating systems that no air should get into the coating materials since it can happen that the material volumes delivered no longer correspond to the volumes required for a coating process.
Upon conclusion of a painting operation, some coating material that has not been applied to the object always remains in the lines. In respect of environmentally friendly techniques, there has been an increasing demand for as much of this material as possible to be recovered. To push material back out of the lines into the respective source without air coming into contact with the material, one of the techniques which has become established is the “pigging technique”, in which material is conveyed through the lines with the aid of a pig, which operates as a sliding body. However, this technique is quite complex, and expensive pig changing devices, pig rinsing stations and the like are required.